1. Field of the Invention
This invention pertains to an apparatus and method for improving the performance of lamps by decreasing the amount of time it takes to reach full lumen output upon lamp starting. More particularly, the invention relates to a uniquely configured container disposed in a fluorescent lamp which maintains mercury vapor equilibrium during lamp operation and prevents mercury diffusion during lamp off periods.
2. Discussion of the Art
Maintaining mercury vapor pressure equilibrium within fluorescent lamps is necessary to maintain optimum lumen output during extended lamp on periods. In conventional fluorescent lamps the mercury vapor pressure increases to an optimum pressure allowing the lamp to reach maximum lumen output. As time passes, the mercury vapor pressure increases to a level above the most preferable pressure causing the luminous flux to decrease. Consequently, a need developed to regulate mercury vapor pressure in fluorescent lamps and thereby achieve peak lumen output for extended periods of time.
To remedy the foregoing situation, amalgams were introduced to maintain the mercury vapor pressure within an optimal range during lamp operation. Upon lamp ignition, the amalgam is heated which causes mercury to diffuse out of the solid and is released into the lamp as vapor. The amalgam achieves mercury vapor equilibrium during lamp operation by supplying the same amount of mercury atoms to the envelope as are spent. However, when the lamp is switched off, the decrease in temperature causes the mercury vapor to navigate to and diffuse into the amalgam causing mercury starvation. The lack of mercury vapor in the lamp envelope during lamp off periods results in low lumens at lamp startup. In order to obtain peak lumens upon lamp ignition without any start-up time penalty, an adequate dose of mercury vapor is required to remain in the lamp envelope during lamp off periods.
To date, no device exists which adequately prevents diffusion of mercury to the amalgam during lamp off periods so that sufficient vapor remains in the lamp atmosphere to provide lamp starting as if no amalgam were present. Continued modifications of the use of amalgams have afforded little success in maintaining sufficient vapor in the envelope when the lamp is turned off.
A recent attempt to remedy this situation is disclosed in U.S. Pat. No. 5,828,169. The amalgam is substantially enclosed by a barrier having an opening that restricts the return of mercury atoms to the amalgam during lamp off periods.
However, the lamp of U.S. Pat. No. 5,828,169 does not eliminate all mercury diffusion. After the lamp is turned off there is still access to the amalgam which allows diffusion of mercury. With extended off times, virtually all of the mercury can diffuse into amalgam. Therefore, the mercury vapor in the envelope decreases after the lamp is turned off thereby affecting the amount of time it takes to reach full lumen output upon lamp ignition.
Thus, a need exists to prevent mercury diffusion in fluorescent lamps so that sufficient mercury vapor remains in the lamp envelope during extended lamp off periods thereby reducing the start up time to reach full lumen output.
A new and improved apparatus and method is provided for regulating mercury vapor equilibrium and decreasing the start up time to reach full lumen output in fluorescent lamps.
In an exemplary embodiment of the invention, the apparatus employs an envelope housing a container having an opening at one end which is selectively opened during lamp operation and closed during lamp off periods.
In a preferred arrangement, a bimetal member is operatively associated with the opening of the container for adjusting the container between an open position and a closed position. A stopping member such as a valve or ball bearing is actuated by the bimetal member and prevents mercury vapor diffusion during lamp off periods. When the lamp is turned on heat is applied to the bimetal member causing the member to deflect. The deflection of the bimetal member releases the stopping member and opens the container allowing the amalgam to maintain vapor pressure equilibrium. When the lamp is turned off, the decrease in temperature causes the bimetal member to contract thereby closing the container and preventing mercury diffusion. As a result, sufficient mercury vapor remains in the lamp envelope during lamp off periods and prevents lamp starting penalties.
A principal advantage of the invention is provided by the peak lumen output during lamp startup time.
Another advantage of the invention resides in the regulation of mercury vapor pressure equilibrium in fluorescent lamps after lamp ignition.
Still another advantage of the invention is provided by increased mercury vapor within the lamp envelope during lamp off periods.